This invention relates to a power switching network for a computer system in which peripheral devices receive power from first and second busses.
Computer systems increasingly include a hierarchy of peripheral devices. The peripheral devices are connected to the host computer through connectors having different configurations.
Electrical connectors and busses interconnect various peripheral devices, particularly computer storage devices. U.S. Pat. No. 5,809,520 Edwards et al. and related patents and applications show and describe various storage devices such as disk drives. Zip(trademark), Zip Notebook, and CLIK!(trademark) drives are typical storage devices which are interconnected in a computer system by electrical cables which have standardized connectors.
The Universal Serial Bus follows a protocol defined in the Universal Serial Bus Specification (USB Spec). The USB Spec provides a standardized approach for peripheral interconnections with a host computer. The USB is set up in a tiered topology with a host on the top tier and USB hubs and functions on subsequent tiers. Each USB device, whether it be a hub or a function, has associated therewith a serial interface engine (SIE) which provides an interface between the hub or function and the transceiver which transmits or receives signals across the serial line. Generally, the SIE takes care of all the USB low level protocol matters such as bit stuffing, cycle redundancy checks (CRCs), token generation, and handshaking. ATAPI is a standard for the connectors, sometimes referred to as Centronics connectors, used to interconnect the peripherals and the host computer.
The IEEE 1394-1995 standard was adopted on Dec. 12, 1995 by the Institute of Electrical and Electronic Engineers, 345 East 47th Street, New York, N.Y. 10017-2394. A copy of that standard is available from the IEEE. The standard is widely known in the industry of digital video, particularly since IEEE-1394-1995, also known as Fire Wire (trademark) (trademark of Apple Computer, Inc., Cupertino, Calif. 95014), has been adopted as the standard for connecting digital video cameras and other digital video devices in the consumer and professional markets. The contents of that standard are incorporated herein by reference (IEEE 1394 Specification).
Peripheral devices, such as the ZIP(trademark), drive may have dual bus capabilities. As an example the busses may be PCMCIA (Personal Computer Memory Card International Association) and USB (Universal Serial Bus). Because each bus is capable of supplying enough power for operation, the system must have circuitry to handle both power supplies and consequently the isolation between each.
The ASIC (Application Specific Integrated Circuit), for such a system is the USB controller which provides the necessary inputs into the power switching circuit to provide seamless transition between either supply.
Accordingly, it is an object of the present invention to provide isolation between the power supplies on the dual busses of a computer system.
In accordance with the present invention a computer system includes peripheral devices which can be connected to first and second busses having first and second power supplies respectively. A power switching network includes first and second solid state switching devices which connect the first power supply to the peripheral device when the second power supply is not connected to the peripheral device. The second power supply is connected directly to the peripheral device and supplies power thereto when it is connected.
Further in accordance with the invention the switching devices are field effect transistors (FET""s) having an inherent body diode. If the user requires the use of the first bus (USB) the controller ASIC provides signals which turn on the FETs in the power switching circuit. Taking advantage of the body diode inherent in the FET""s, the controller is immediately powered, after which the signal the controller signal drives the input to the first FET, providing the controller regulators with a full supply. After the host computer has xe2x80x9cenumeratedxe2x80x9d and allowed for full power operation, the signal from the controller then drives the input to the second FET, thereby powering the rest of the drive. Also, if the USB requires the peripheral to sleep, enough voltage is provided to turn the FETs off and suspend the drive for power consumption purposes. Two components, (a capacitor and a resistor) on the gate of the second FET provide a time constant to slowly ramp the voltage to limit the inrush current from the USB supply.
In a similar manner, if the user requires the use of PCMCIA, then agin the invention utilizes the body diode (eliminating the need for alternate components) of the first and second FETs to protect the USB from a back power condition and provide controller power.
The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and dependent claims.